If there is a particular flavor of Linux that should be specified in the Version drop-down list, please say so here. Otherwise I’m just choosing “Other Linux (64-bit)” here and will hope for the best.
Dave’s context is very much worth adding, that StartOS is based on Debian. If doing something with StartOS that at any time requires specific steps/instructions for a flavor of Linux, the Debian/Ubuntu/Mint etc way would be the way to go.